In case of a broadband communication system, more effective transmission and reception schemes in time, space and frequency domains and their application methods have been suggested to maximize efficiency of limited radio resources. In particular, an orthogonal frequency division multiplexing (OFDM) scheme based on multiple carriers is advantageous in that spectral efficiency can be maximized through selective scheduling in a frequency domain using different channel features of subcarriers along with reduction of complexity in a receiver under an environment of frequency selective fading generated in a broadband channel. In addition, the OFDM scheme has received attention as a scheme for enhancing efficiency of radio resources in a frequency domain as the OFDM scheme can be enlarged into an OFDMA scheme through allocation of different subcarriers to a plurality of users. Examples of the standardizations based on OFDMA include IEEE 802.16-2004 which is defined to target fixed subscriber mobile stations in IEEE 802.16 of IEEE (Institute of Electrical and Electronics Engineers) and IEEE 802.16e-2005 correction standardization for providing mobility of subscriber mobile stations. These standardizations adopt a time division duplex (TDD) scheme as a duplexing scheme for dividing an uplink from a downlink. The TDD scheme allocates different time domains to respective links and uses the same frequency band for a corresponding time period, wherein each of the time domains is divided by a guard time. Although the TDD scheme cannot transmit data to the uplink and the downlink simultaneously, it dynamically allocates uplink and downlink time domains. Accordingly, the TDD scheme has excellent flexibility and thus is suitable for asymmetrical transmission. Also, the TDD scheme has drawbacks in that since the uplink and the downlink are divided from each other depending on time, exact synchronization between base stations is required, a cover domain is reduced due to delay in propagation, and it is difficult to support a moving speed of high speed. However, the TDD scheme is advantageous in that smart antenna, link adaptive scheme, and line compensation scheme are easily applied to the TDD scheme due to asymmetrical channel features of the uplink and the downlink. Thus, link budget can be improved through this advantage.
FIG. 1 illustrates a logical frame structure of the legacy IEEE 802.16e system. As shown in FIG. 1, the logical frame structure of the legacy IEEE 802.16e system includes a preamble, a frame control header (FCH), a control signal unit of a downlink/uplink MAP (DL/UL MAP), and a data burst. Data transmission of each user is defined by different subcarrier allocation schemes (PUSC, (O-) FUSC, TUSC, AMC, etc.) depending on a method for configuring subchannels. Various permutation zones can be configured within one frame. Also, a transmit transition gap (TTG) (121.2 μs) and a receive transition gap (RTG) (40.4 μs) which are guard time periods for dividing uplink transmission time from downlink transmission time are inserted between the downlink and the uplink in the middle of the frame and at the last of the frame.
The preamble is used for initial synchronization, frequency offset, channel estimation, and cell ID acquisition (cell retrieval). The FCH provides channel allocation information and channel coding information, which are related to the DL-MAP. The DL/UL-MAP provides channel allocation information of the data burst in the uplink and the downlink.
FIG. 2 illustrates a frame structure which includes multiple permutation zones in accordance with a subchannel allocation mode of the legacy IEEE 802.16e system.
In the logical frame structure except for the preamble, a subchannel allocation mode is selected considering frequency diversity gain, scheduling gain, pilot overhead, or easiness in application of multiple/adaptive antennas. Various permutation zones are configured through zone_switch_IE in the MAP. Examples of the subchannel allocation mode include a Full Usage SubChannel (FUSC) mode, an Optional-FUSC mode, a Partial Usage SubChannel (PUSC), a diversity subchannel mode, and an adaptive modulation and coding (AMC) subchannel mode. In FIG. 2, a zone X is necessarily required per frame, and a zone Y may be required per frame if necessary.
For example, in the DL-MAP, a base station transmits DIUC=15 which includes STC_DL_ZONE_IE( ) to indicate a specific permutation and a transmission diversity mode, which should be required for later allocation. In the UL-MAP, the base station transmits UIUC=15 included in UL_ZONE_IE( ) to report that a specific permutation should be used for subsequent allocation. A data transmission interval (burst) of the downlink is divided into a PUSC subchannel interval, a diversity subchannel interval, and an AMC subchannel interval. A data transmission interval (burst) of the uplink is divided into a diversity subchannel interval and an AMC subchannel interval.
FIG. 3 illustrates a resource structure of the IEEE 802.16e system within a random continuous or dispersed band.
A preamble, an FCH, and a DL-MAP are necessarily required for transmission and reception of each frame. In this case, exact acquisition of data or control information within the frame is performed. When considering the aforementioned frame structure of the IEEE 802.16e system, the legacy 802.16e system is configured and operated within a random frequency band as illustrated in FIG. 3A and FIG. 3B. As illustrated in FIG. 3A, a single mode of the IEEE 802.16e system can use a frequency band through repetition of the legacy structure within the continuous or dispersed band. As illustrated in FIG. 3B, a dual mode which exists along with a new system mode is configured by an independent resource structure through separate channel allocation. In FIG. 3B, ‘B’ represents a zone where the legacy IEEE 802.16e system is operated, and ‘A’ represents a zone where a new evolution system is operated.
However, when considering resource allocation and frame structure of the IEEE 802.16e system, a simultaneous use of the legacy system mode and the new evolution system mode within a random allocation band is repeated or needs independent signal processing. In this case, a problem occurs in that it is difficult to use limited radio resources effectively. Particularly, as overhead of a control signal such as FCH or DL-MAP at the front of the frame is repeatedly used, data transmission capacity of the system is reduced. Also, it is difficult to configure flexible channels within various bandwidths in application of the new evolution system mode. Accordingly, a data communication method of a flexible channel structure and a flexible frame structure is required, which maximizes efficiency of time-frequency resources and at the same time covers the new evolution system effectively and enables the new evolution system to be independently functioned in a multiple access system, which uses multiple frequencies, such as the legacy IEEE 802.16e system.